Enhancing high harmonic generation in GaAs by elliptically polarized light excitation

High harmonic generation (HHG) in solids shows interesting behavior owing to their crystal structures. Here, the authors investigate a prominent example: HHG in GaAs can be enhanced by elliptically polarized light excitation. Remarkably, the enhancement is accompanied by emergent nonlinear optical activity, and it become salient only at particular ``intermediate'' excitation strengths. These results indicate that the key for HHG enhancement lies in the interference among nonlinear emission processes, revealing that not only material properties but optimal-strength excitations are important for controlling HHG properties via fine-tuning of the nonlinear dynamics.